Sheet material, such as sheet steel which is sold in a coiled roll, is sold by the pound. The length of the roll of material is calculated using the density of the steel, roll weight and gauge. Variations in the nominal gauge of the steel lead to unacceptable errors in length calculations. It has been found, for example, that 0.26 gauge galvanized sheet steel varies in thickness between 0.0187 and 0.0247, and 30 gauge galvanized sheet steel varies between 0.0127 and 0.0187. These variations in thickness provide unacceptable errors in the present way in which the length is calculated. For example, due to non-uniformity in the thickness of the steel, a 5 on roll of 48" width 28 gauge galvanized steel can vary in length between 3,808 feet and 4,864 feet. Thus, there can be a considerable difference in the length of two like gauge and like weight rolls of steel. Coiled rolls of sheet metal are bought by the pound and then the sheet metal is used by the square foot to manufacture various products. Difference in the length of the rolls is critical in the use of the sheet metal in calculating the cost of items manufactured from the sheet material.